Drug development company Acelyrin Inc. recently saw a modest increase in its stock price after announcing the adoption of a shareholder rights plan in connection with an unsolicited offer from Concentra Biosciences and Tang Capital Partners, its controlling shareholder.

Acelyrin, based in Agoura Hills, saw an increase in share price of just above 2% from the closing price of $2.69 on March 13 to a close of $2.75 on March 14. The company announced the plan, also known as a poison pill, on March 13.

The rights plan is effective immediately and will expire on March 12 of next year.

The unsolicited offer, received on Feb. 20, sent Acelyrin’s share price up by nearly 20% from a close on Feb. 20 of $2.17 to a close of $2.60 the following day. Concentra in San Diego offered to acquire all of the outstanding shares of Acelyrin for $3 per share in cash.

Shares closed at $2.77 on March 20.

Proposed merger with Alumis

The offer came about two weeks after Acelyrin and Alumis Inc. in South San Francisco announced an agreement to merge in an all-stock transaction. The transaction is expected to close in the second quarter, subject to approval by the stockholders of both companies.

The combined company will operate under the Alumis name with its corporate headquarters remaining in South San Francisco.

Martin Babler, chief executive of Alumis, said that his company and Acelyrin together will “advance breakthroughs for patients and drive long-term value for stockholders” by creating a “leading” clinical stage biopharma company in immune-related diseases.

“The combined company will have a significantly strengthened financial position to support a highly differentiated and diverse pipeline with multiple catalysts,” Babler said in a statement. “With our management team’s successful track-record of developing innovative therapies and an extended runway afforded by combining with Acelyrin, the transaction will allow us to unlock the value of the combined portfolio for current and future investors and address what we believe is a current dislocation with our valuation.”

Acelyrin Chief Executive Mina Kim said that the company’s board is confident that the all-stock deal with Alumis maximizes long-term value for its shareholders and continues to recommend that they support the planned merger.

“We chose to enter into the merger agreement with Alumis after a comprehensive assessment of strategic alternatives and believe this is the best outcome for Acelyrin stockholders,” Kim said in a statement.

In a March 4 release, Acelyrin said its board of directors believed that the unsolicited indication of interest from Concentra and Tang Capital “is not reasonably expected to result in a superior proposal to the planned merger with Alumis Inc.”

Guggenheim Securities LLC in New York served as financial adviser to Acelyrin and Paul Hastings LLP in downtown and Fenwick & West LLP in Mountain View were its legal counsel.

Acelyrin’s lead drug in development is lonigutamab, a subcutaneously delivered monoclonal antibody being studied for the treatment of thyroid eye disease.